The present invention generally relates to vascular support garments. More specifically, the present invention relates to counter pressure garments that can be used in low pressure environments such as outer space.
In environments having very small or no ambient gas pressure, such as high altitude or the vacuum of space, a subject's respiration and circulatory balance are of concern. Gas needs to be delivered to the subject's lungs at a high enough pressure to cause diffusion of oxygen into the blood. It has been found that a gas pressure of about 80 mm Hg is minimally needed for proper breathing. An oxygen pressure of about 160 mm Hg is normally experienced at sea level. For the current design of the NASA Extravehicular Mobility Unit (EMU) spacesuit, the oxygen pressure is about 222 mm Hg.
As ambient gas pressure rises, blood pressure similarly rises. But tissue pressure that substantially matches the blood pressure must exist. Otherwise, the circulating blood can rush into low pressure areas and pool. If tissue pressure is not sufficiently high, the veins (and particularly the small ones) will become engorged with blood. As venous engorgement continues, pressure within the veins and capillaries continues to increase. If the pressure exceeds about 10 mm Hg, measurable amounts of excess fluid can be forced through the capillary walls and accumulate in the tissues. The accumulation of fluid can result in edema and a decrease in the circulating blood volume.
To provide adequate pressure in the tissue to prevent pooling, various suits have been employed to provide a counter pressure on the tissue. In the context of space, one such suit has been a "full pressure suit." It is a gas filled pressure suit that is anthropomorphically shaped, gas-tight, and pressurized with oxygen. Typically, these suits have used a rigid but flexible pressure restraining outer garment. Another type of suit has been referred to as a "partial pressure suit." Therein, an elastic or inelastic outer garment typically covers bladders that are filled with a gas. The bladders, together with the garment, can then apply constant counter pressure to the body. In contrast, a full pressure suit does not typically contain bladders since the pressure within the suit can provide the counter pressure. Usually, the bladders in the partial pressure suits are not pre-pressurized with a gas. Rather, they are filled with air or nitrogen from a gas pressure source that is external to the bladders. And the bladders are filled after the garment has been donned. Also incorporated under the inelastic garment of some partial pressure suits are tubes or capstans running over the limbs and trunk. As with the above bladders, the tubes are not pre-pressurized with gas. Thus, they too must be inflated after donning to apply counter pressure to the body.
While addressing some of the physiological concerns, the full pressure suits have posed various problems. There is a relatively high energy cost of activity. Gas pressurized limbs and torso cause severe restrictions in mobility. Body temperature regulation due to the impermeability of the suit necessitates elaborate cooling systems. And with the need for pressurized gas within the suit, a danger with leaks resulting from ruptures or tears exits. Due to the complexity of the surface and small size of a hand, bulky gas pressurized gloves severely limit dexterity and tactility.
In part to minimize the disadvantages associated with high energy cost and restricted mobility in gas filled suits, a space activity suit (SAS) or partial pressure suit was developed with elastic material which itself provided counter pressure to the body. The partial pressure suit also allowed direct evaporation of sweat in the absence of the type of cooling system associated with a gas filled suit. Also, the partial pressure suit has tended to be less bulky than the full pressure suit, thereby increasing mobility.
Notwithstanding its advantages, the partial pressure suit still has drawbacks. For example, if a counter pressure is to be evenly applied around a circumference, a body part must be perfectly circular. But the body is not circular, and is instead ovate, ellipsoidal and irregular. Areas of the body that are far from circular include the hands, which have a concave palm and a convex dorsum. Further, body radii in muscular areas change during contraction and relaxation. And with noncircular and/or muscular areas, the suit material has a tendency to gap away from the body, even when the material is elastic. In the specific context of the hand, the elastic material tends to primarily press at the outer edge of the hand and, accordingly, leave the dorsum and palm without significant counter pressure.
One effort to address the problem of gaping has included the use of a single oil filled bag at the dorsum to fill the void in the gap. Similarly, a bladder has been filled with gas from an external source and thereby applies a counter pressure to the dorsum. But when such a bag or bladder is used in the glove of a suit, fluid accumulation has only been reduced, not substantially eliminated. That has been especially so in the palm area of the hand. Perhaps more importantly, the need for a constant external gas source to a bladder can significantly affect reliability. Also, as the need for more counter pressure increases, so does the need for a bag that is larger and/or nonpliable. However, as the bag increases in size and/or stiffness, dexterity and tactility decrease. Additionally, increased size and stiffness makes donning and doffing more difficult.
As can be seen, there is a need for an improved counter pressure garment and, specifically, a glove for low pressure environments, such as outer space. Also needed is an improved counter pressure glove that can provide a counter pressure of about 222 mm Hg, which is the breathing pressure inside the most conventional full pressure suit. A further need is for a garment that can provide counter pressure to blood supplied tissue that is significantly noncircular in shape and subject to frequent contraction, such as a human hand. Another need is for a space suit glove that not only provides adequate counter pressure to the palm of a hand but is also relatively easy to don and doff. Yet another need is for a method of equalizing a breathing pressure and tissue pressure in the palm of a hand.